Need help with tempermental water pump

[Rohan]

Hoping someone can help me figure this out.



Short version - my engine (2006 Yanmar 3YM30) won't pump water properly unless I first give the pump a push.



Long version - started engine the other day but no water was coming out. Of course I went through every troubleshooting step - checked the seacock was open, checked the hoses, checked the filter, checked the water pump belt (which is less than a year old), checked the impeller (which was brand new). Check to make sure everything was sealed, no air leaks. Everything seemed good. Since I just put in a new impeller this week, I swapped the old one back in just in case there was something wrong with the new one. Still no dice. Engine ran and I revved the engine up but the water pump wouldn't turn.


Out of desperation (?) I poked at the water pump belt with a screwdriver while the engine was running to help it along. And then it started spinning on its own and pumping water normally!



Anchored overnight, tried again in the morning and same problem. Again the engine started fine but water pump wouldn't spin unless I prompted it.



So - what the heck? Any suggestions? I don't want to do this every time I use the engine.

[sailorboy1]

loose or worn out belt

[Rohan]

Originally Posted by sailorboy1

loose or worn out belt

Belt is still basically brand new.



It is a little loose, but it's always been that way. In fact, I don't think there is a way to tighten it. The only place that could be an adjustment hinge is welded down.

[s/v Jedi]

You mean you replaced impellers while seeing the belt slipped over the pulley? I thought I had seen it all

[osprey877]

[QUOTE=Rohan;3892462it. The only place that could be an adjustment hinge is welded down.[/QUOTE]

You adjust the tension by adding/removing shim’s between the two halves of the pump pulley. But You should first replace the belt with a new one before making any adjustments . You will have to take the pulley apart to get the old one off and you will then see the metal discs that you make any adjustments with if the new belt doesn’t fix the problem.

[barnab]

If the loise belt was able to start the pump but not anymore there could be two reasons
- it is worn too much and needs to be replaced
- there is more friction to overcome so the belt cannot handle it anymore...maybe the pumps bearings are deteriorating

[Rohan]

Originally Posted by s/v Jedi

You mean you replaced impellers while seeing the belt slipped over the pulley? I thought I had seen it all

Nothing else is working, so I had nothing to lose by trying.

[skipperpete]

Originally Posted by osprey877

You adjust the tension by adding/removing shim’s between the two halves of the pump pulley. But You should first replace the belt with a new one before making any adjustments . You will have to take the pulley apart to get the old one off and you will then see the metal discs that you make any adjustments with if the new belt doesn’t fix the problem.

Not on a 3YM ya don’t, there’s a slot in the bracket on the inside and a nut you loosen to adjust the pump. A worrying possibility is that the pulley is loose on the shaft and its sitting high on the two flats that cause it to rotate. Check the tightness of the pulley retaining nut….. easy to say, not so easy to do if the front of the engine has poor accessibility.